This invention relates to spring units for use in mattresses, spring upholstered furniture and the like, and to a method and apparatus for manufacturing such spring units. The invention also relates to a spring interiors comprised of a plurality of such spring units.
In our International Patent Application number WO90/01285, we have disclosed a spring unit comprising a continuous coil spring contained within a sleeve of strong, yet flexible, material. In one of the arrangements described in WO90/01285 a separately formed sleeve of calico material is carried on a tubular former and a band of continuous coil spring is drawn off a reel, through one end of the former and out the other end. As the band passes through the former it draws off the sleeve from the former and entrains it around itself. In another arrangement described in WO90/01285 a continuous sheet of calico is carried on a reel and the band of continuous coil spring in wound on a reel. The free ends of the calico material are drawn through a V-shaped former which serves to direct the sides of the sheet up and around the band. The sides of the calico are drawn together above the former and are stitched together.
In the former arrangement additional steps are required in separately forming the sleeve and loading the sleeve onto the former before the sleeve can entrain itself around the band. In the latter arrangement, in which the sleeve is formed simultaneously with entrainment around the band, difficulty is experienced in applying an even compression to the continuous coil spring as the material is wrapped around it.
According to our invention a spring unit comprising a continuous coil spring contained within a sleeve of strong, yet flexible, material is produced by providing a folding attachment device having oppositely inclined spaced walls which converge from a feed end to an outlet end, and simultaneously drawing the flexible material and the coil spring through the folding attachment device from the feed end to the outlet end with the spaced walls acting to fold the material over the coil spring and to apply a substantially uniform compressive force to the coil spring whereafter as the material and the coil spring are drawn through the outlet end, overlapping edges of the flexible material are joined together to form the sleeve and complete the spring unit.
The provision of the attachment device enables us to produce spring units in a continuous operation, with a substantially uniform compressive forced applied to the spring.
The inclined walls are interconnected at one pair of adjacent edges by a support plate which supports the flexible material, and the material is fed through a gap at the feed end of the folding attachment device between the support plate and a guide bar which ensures the material does not buckle or crease as it is drawn through the folding attachment device, the material being folded over the coil spring as the material and the coil spring exit from the outlet end of the folding attachment device.
The overlapping edges of the material may be joined together by any convenient method. For example they may be stitched, glued, or heat welded together. The flexible material may comprise a single layer of the strong yet flexible material, such as calico, which is drawn through the folding attachment from the reel. Alternatively the material may be of composite construction comprising inner and outer layers of fabric with an insulator layer sandwiched therebetween. Such material may be preformed. Preferably, however, the three layers are drawn through the folding attachment device from separate, individual, reels.
When the overlapping edges of the flexible material are stitched together following exit from the folding attachment device, a sewing head is disposed between first and second variable speed puller feed mechanisms which act to drawn the material and the spring through the folding attachment device and act to tension overlapping edges between spaced stations for joining them together by the sewing head.
Conveniently both feed mechanisms co-operate with the overlapping edges of the fabric on opposite sides of the sewing head to maintain the edges in overlapping relationship for the sewing operation and to ensure the compressive force applied to the coil spring by the relative inclination of the spaced walls of the folding attachment is maintained.
The folding attachment device may be positioned with the support plate generally vertical and the inclined walls comprising upper and lower walls. This facilitates assembly since the sewing head produces a side seam, and the flexible material and a continuous coil spring are drawn from reels rotatable about generally vertical axes.
The spring unit produced by a continuous operation is of infinite length and is then cut to required lengths for the construction of mattresses and the like, as otherwise described in WO90/01285.